Molecular conformations and rotation barriers of 2-halogenoethanethiols and 2-halogenoethanols: an ab initio study

Abstract

The molecular geometries of all the possible conformations of 2-halogenoethanethiols and 2-halogenoethanols (F, Cl, Br, I) have been fully optimized at the ab initio MP2/6–31G** level (for Br and I the LANL1DZ basis was adopted). Whilst for all 2-halogenoethanols and for 2-fluoroethanethiol the Gg′ structure was found to be the most stable, the Tg rotamer is favoured for 2-chloro-, 2-bromo- and 2-iodo-ethanethiols. In these latter molecules the hydrogen-bond strength seems to be insufficient to overcome the non-bonded repulsive interactions and to stabilize the Gg′ conformer. The rotation barriers around the C(1)–C(2) bond are rather high, whilst those concerning the SH and OH groups are generally small and of similar size.